The present invention relates to a room temperature curable silicone rubber composition or, more particularly, to a room temperature curable silicone rubber composition useful as a sealing material in building works without the disadvantage of causing stain thereon and therearound.
As is well known, various types of room temperature curable silicone rubber compositions, i.e. liquid or pasty compositions curable at room temperature into a rubbery elastomer, are manufactured and widely used in a variety of application fields. The cured rubbery elastomers obtained from the room temperature curable silicone rubber composition (referred to as RTV hereinbelow) are widely used by virtue of their excellent properties such as weathering resistance, durability, heat and cold resistance and the like. In particular, RTV compositions are widely used in building works as a sealing material or an adhesive between glass-made parts, between glass and a metal, concrete joints and others. More particularly, RTV compositions capable of giving a cured elastomer having a low elastic modulus and large elongation are used as a sealing material of joints where a relatively large relative displacement of the building members is expected. RTV compositions of this type are called a silicone sealant and demand thereof is rapidly increasing year by year.
One of the serious problems in these silicone sealants is the susceptibility of the cured elastomer thereof to surface stain which is presumably due to the remarkable susceptibility of the organopolysiloxane as the principal ingredient of RTV compositions to accumulation of static electricity to attract floating dusts in the atmosphere. Therefore, the aesthetic appearance of buildings constructed using a silicone RTV is lost within a relatively short period due to the stain on the cured elastomer of the silicone sealant. Moreover, deposition of stain is sometimes not limited to the surface of the cured RTV but the stain may propagate or spread over the surfaces of the members adjacent to the sealed joint. This problem is most serious when the members adjacent to the sealed joint are made of a natural stone such as granite and marble.
With an object to solve this problem, an improved RTV composition has been recently proposed by compounding a silicone RTV with a surface active agent having polyoxyethylene groups, sorbitan residues or disaccharide residues in the molecular structure (see, for example, Japanese Patent Kokai No. 56-76452). The desired effect of stain prevention, however, in this type of silicone RTV compositions can be obtained only when the amount of the surface active agent formulated therein is considerably large so that a disadvantage is sometimes unavoidable that the adhesive strength between the sealant and the substrate surface, which is an important property for a sealant, is greatly decreased.
For providing a further improvement of the above mentioned silicone RTV compositions admixed with a surface active agent, it has been proposed to formulate a silicone RTV with a surface active agent having at least one fluorine atom in a molecule (see Japanese Patent Kokai No. 58-167647). According to this further improvement, the amount of the surface active agent can be greatly reduced so that the above mentioned drawback of the decrease in the adhesive strength can be mitigated though with another problem that the durability of the stainpreventing effect is not always satisfactory.